10 PHYSIOLOGY OF BACTERIA 



Normally chlorophyl plants do not excrete protein 

 cleavage products. There are many observations indi- 

 cating that green plants in the dark not only break down 

 their carbohydrates, but also their proteins. Yet, 

 their synthetic action seems to be so powerful that all 

 the products of nitrogenous catabolism are re-utilized 

 somewhere in the plant, and do not leave it. 



Differing from this endogenous catabolism of the 

 starving organism is the autolysis of the dead organism. 

 When tissues of a dead animal are held at 37°C. under 

 aseptical conditions, the protein readily breaks down to 

 simpler compounds. This self-digestion or autolysis 

 of tissues is due to proteolytic endoenzymes. The 

 products of autolysis are in a general way compar- 

 able to the products of peptic or tryptic digestion, and 

 are quite different from the products of endogenous 

 catabolism. 



Another difference between the two processes of 

 protein decomposition lies in the rate of the process. 

 As an example, Jacoby (1900) observed that normal 

 liver of a dog, after twenty-four hours of autolysis, had 

 lost 17.9% of the total nitrogen, or 20% of the protein 

 nitrogen. This is an enormous rate compared with the 

 0.6% of nitrogen loss by endogenous catabolism by 

 a starving man per day. 



It is quite necessary to differentiate sharply between 

 these two different processes. This distinction was not 

 made by Rubner (1913), but is drawn very sharply by 

 Euler (Euler-Lindner, 1915): 



"Yeast contains plenty of proteinases and peptases. In the living 

 cell, the destructive action of these is in adjustable equilibrium with 

 the construction of protein. If, however, synthesis is retarded in 

 comparison with the cleaving action of the digestive enzymes, we 

 observe the phenomenon which is usually called autolysis . . . 



